Here I’ve used the dominant color to add search engine tabs to the bottom of the screen. Normally they’re hidden away, but when you first install the restartless add-on, all the tabs appear for a few seconds. You can also see that all installed search engines are available, such as the one for Twitter Address Bar Search.

Selecting text shows colored tips

When you select some text or start typing in a text box (including those in the Firefox interface like the AwesomeBar!), the tabs will peek up from below only to show their transparent color-filled tips. If you do point at one of the tabs, it’ll become fully opaque and pop up to show the icon. Clicking it will let you search for whatever you have selected or typed.

After installing the add-on, hold shift while pointing at an image to have it report the color and show it behind the image. One slight difference from Margaret’s code is that color and transparency values are rounded down to a multiple of 16.